title: Knockout of spinophilin, an endogenous antagonist of arrestin-dependent alpha2-adrenoceptor functions, enhances receptor-mediated antinociception yet does not eliminate sex-related differences.
abstract: We have previously shown gonadal steroid-dependent, gender specific modulation of nociception by alpha(2)-adrenoceptors. Agonist activation of the receptor enhances its association with spinophilin that antagonizes arrestin functions both by diminishing receptor phosphorylation by G-protein-coupled receptor kinase 2 (GRK2) and by competing for receptor interactions with arrestin. Since spinophilin is highly enriched in dendritic spines, we investigated whether alpha(2)-adrenoceptor-induced antinociception as well as sex-related differences are modified in spinophilin knockout mice. We evaluated alpha(2)-adrenoceptor antinociception in a heat-evoked tail flick test in spinophilin wild type (Sp(+/+)) and knockout (Sp(-/-)) mice. Baseline tail flick latencies (TFLs) did not change between any groups. Interestingly, the alpha(2)-adrenoceptor agonist, clonidine, increased TFL in male and diestrous (low estrogen) Sp(-/-) as well as Sp(+/+) mice; in fact, this increase in TFL was significantly higher in Sp(-/-) male and diestrous groups than in their Sp(+/+) counterparts. This unexpected finding is consistent with enhanced alpha(2)-adrenoceptor-mediated sedation observed previously in Sp(-/-) mice, presumably due to accelerated endocytosis of desensitized receptors and recycling of refreshed receptors when arrestin is not competed for by spinophilin in Sp(-/-) mice. Despite modulation of alpha(2)-adrenoceptor effects in Sp(-/-) mice, sex-related differences were retained; thus, clonidine was ineffective in proestrous females (highest estrogen levels), in both Sp(-/-) and Sp(+/+) mice, reaffirming that estrogen suppresses alpha(2)-adrenoceptor-evoked antinociception. These findings show that elimination of spinophilin enhances alpha(2)-adrenoceptor-evoked antinociception in estrogen-deprived physiological settings, suggesting a role for spinophilin to suppress these effects, and yet this enhanced response cannot overcome the absence of antinociception with elevated estrogen levels.
authors.affiliation: Department of Neurobiology and Neurotoxicology, Meharry Medical College, 1005 D.B. Todd Boulevard, Nashville, TN 37208, USA.
authors.forename: Subodh
authors.initials: S
authors.lastname: Nag
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
authors.forename: Lee E
authors.initials: LE
authors.lastname: Limbird
authors.forename: Sukhbir S
authors.initials: SS
authors.lastname: Mokha
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D019393:Arrestin / Q000037:antagonists & inhibitors / Q000378:metabolism; D003000:Clonidine / Q000008:administration & dosage / Q000494:pharmacology*; D004967:Estrogens / Q000378:metabolism / Q000502:physiology; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000172:deficiency* / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000235:genetics; D010146:Pain / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism* / Q000502:physiology; D012737:Sex Factors; D000099273:Neurabins
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D019393:Arrestin; D003000:Clonidine; D004967:Estrogens; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D018341:Receptors, Adrenergic, alpha-2; D000099273:Neurabins